Redundant measurement of pseudo differential pressure using absolute pressure sensors

ABSTRACT

Apparatus and associated methods relate to generating redundant measurement of pseudo differential pressure using two absolute-pressure sensors, each exposed to a different environment. Each of the two absolute-pressure sensors has complementary first and second output nodes. The first output node has a positive relation with and/or response to increasing pressure, while the second output node has a negative relation with and/or response to increasing pressure. A first difference measurement signal is calculated based on a difference between the positive relation output signals of the first and second absolute-pressure sensors. A second difference measurement signal is calculated based on a difference between the negative relation output signals of the first and second absolute-pressure sensors. Both the first and second difference measurement signals are indicative of a pressure difference between the first and second environments. Such redundant measurement of differential pressure can advantageously provide continuous pressure-difference measurement in spite of various component failures.

BACKGROUND

Differential pressure sensors are used to measure a difference betweenpressures of two fluid environments. These two fluid environments may belocated nearby one another or at great distance one from another.Differential pressure sensors come in at least two varieties: i) truedifferential pressure sensors; and ii) pseudo differential pressuresensors. True differential pressure sensors provide fluid communicationbetween each of the two environments and to each of two sides of adifferential pressure transducer, respectively.

Pseudo differential pressure sensing can be accomplished using twodistinct absolute pressure sensors. Each absolute pressure sensor isexposed to one of the two fluid environments so as to measure that fluidenvironment's absolute pressure. By taking the difference of resultingsignals indicative of absolute pressures of the two fluid environments,a signal indicative of a difference between the two absolute pressurescan be generated.

Various types of pressure sensors have various advantages anddisadvantages. In some circumstances, for example, it may be undesirableto expose both sides of a differential pressure sensor to highpressures. In such cases, a pseudo differential pressure sensor may bepreferable to a true differential pressure sensor. In some cases, thetwo fluid environments may be located at a great distance one fromanother. In such cases, use of two remote absolute pressure sensors mayprovide a good solution for measuring a pressure differential.

Failure of a differential pressure sensor can be problematic in someapplications. If, for example, one of the two bridges of a differentialsensor has a sensor failure, then the differential pressure sensor isrendered incapable of measurement of differential pressure. Failure tomeasure a differential pressure can cause a system to perform poorly orto cease performance altogether. Suboptimal performance can waste moneyand/or present a danger to people. For some such systems where thesedeleterious consequences can arise, improved sensor reliability canprovide increased safety and/or prevent wasted expenses.

SUMMARY

Apparatus and associated methods relate to a system for providingredundant measurement of pseudo differential pressure. The systemincludes a first absolute-pressure sensor exposed to a firstenvironment. The first absolute-pressure sensor includes a plurality ofpressure transducers configured in a first Wheatstone bridge. The firstWheatstone bridge has first and second output nodes that operationallygenerate output signals that increase and decrease, respectively, inresponse to increasing pressure of the first environment. The systemincludes a second absolute-pressure sensor exposed to a secondenvironment. The second absolute-pressure sensor includes a plurality ofpressure transducers configured in a second Wheatstone bridge. Thesecond Wheatstone bridge has third and fourth output nodes thatoperationally generate output signals that increase and decrease,respectively, in response to increasing pressure of the secondenvironment. The system includes a first difference calculatorelectrically coupled to the first and third output nodes of the firstand second absolute-pressure sensors, respectively. The first differencecalculator generates, based on a difference between the output signalsof the first and third output nodes, a first measurement signalindicative of a pressure difference between the first and secondenvironments. The system includes a second difference calculatorelectrically coupled to the second and fourth output nodes of the firstand second absolute-pressure sensors, respectively. The seconddifference calculator generates, based on a difference between theoutput signals of the second and fourth output nodes, a secondmeasurement signal indicative of the pressure difference between thefirst and second environments.

Some embodiments relate to a system for providing redundant measurementsof pseudo differential pressure. The system includes first and secondabsolute-pressure sensors configured to measure a pressure of first andsecond environments, respectively. Each of the first and secondabsolute-pressure sensors includes an elastically deformable membraneconfigured to deform in response to exposure to an environment having apressure. Each of the first and second absolute-pressure sensorsincludes a first piezoresistor located on a first surface region of theelastically deformable membrane. The first surface region becomesincreasingly convex in response to increasing pressure. Each of thefirst and second absolute-pressure sensors a second piezoresistorlocated on a second surface region of the elastically deformablemembrane. The second surface region becomes increasingly concave inresponse to increasing pressure. The first piezoresistors of both thefirst and second absolute-pressure sensors are electrically configuredin a first Wheatstone bridge operatively generating a first measurementsignal indicative of a pressure difference between the first and secondenvironments. The second piezoresistors of both the first and secondabsolute-pressure sensors are electrically configured in a secondWheatstone bridge operatively generating a second measurement signalindicative of the pressure difference between the first and secondenvironments.

Some embodiments relate to a method for providing redundant measurementsof pseudo differential pressure. The method includes exposing a firstabsolute pressure sensor to the first environment having the firstpressure. The method includes exposing a second absolute pressure sensorto the second environment having the second pressure. The methodincludes generating first and second output signals, each indicative ofthe first pressure of the first environment. The method includesgenerating third and fourth output signals, each indicative of thesecond pressure of the second environment. The method includescalculating a first difference signal between the first and third outputsignals. The method includes calculating a second difference signalbetween the second and fourth output signals. The method includesselecting a measurement signal from among the first and seconddifference signals for use as a signal indicative of a pressuredifference between the first and second environments. The method alsoincludes outputting the selected measurement signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a fluid filter system providingredundant measures of pseudo differential pressure usingabsolute-pressure sensors on either side of a fluid filter.

FIG. 2 is an electrical schematic of two absolute pressure sensorsconfigured to provide redundant measures of pseudo differentialpressure.

FIGS. 3A and 3B are side elevation views of an exemplary MEMS absolutepressure sensor, without and with a positive external pressure,respectively.

FIG. 4 is a perspective view of an exemplary pseudo differentialpressure sensor configured as a Wheatstone bridge.

DETAILED DESCRIPTION

Apparatus and associated methods relate to generating redundantmeasurement of pseudo differential pressure using two absolute-pressuresensors, each exposed to a different environment. Each of the twoabsolute-pressure sensors has complementary first and second outputnodes. The first output node has a positive relation with and/orresponse to increasing pressure, while the second output node has anegative relation with and/or response to increasing pressure. A firstdifference measurement signal is calculated based on a differencebetween the positive relation output signals of the first and secondabsolute-pressure sensors. A second difference measurement signal iscalculated based on a difference between the negative relation outputsignals of the first and second absolute-pressure sensors. Both thefirst and second difference measurement signals are indicative of apressure difference between the first and second environments. Suchredundant measurement of differential pressure can advantageouslyprovide continuous pressure-difference measurement in spite of variouscomponent failures.

FIG. 1 is a schematic diagram of a fluid filter system providingredundant measures of pseudo differential pressure usingabsolute-pressure sensors on either side of a fluid filter. In FIG. 1,system 10 is configured to monitor a pressure difference across fluidfilter 12 to determine if fluid filter 12 is permitting fluid conductiontherethrough. System 10 includes input port 14, output port 16, fluidconductor 18, fluid filter 12, upstream pressure sensor 20, downstreampressure sensor 22, difference calculators 24 and 26, sensor failuredetector 27, controller 28, bypass fluid conductor 30, and bypass valve32. Fluid filter 12 is located between input port 14 and output port 16within fluid conductor 18. As fluid filter 12 removes contaminantswithin a fluid flowing within fluid conductor 18, fluid filter 12 canbecome less conductive of fluid flow. If fluid filter 12 becomes socontaminated that the fluid conductivity between input port 14 andoutput port 16 falls below a specified threshold, a process that usessystem 10 can fall out of specification. When the conductivity fallsbelow the specified threshold, controller 28 can temporarily open bypassvalve 32 so as to permit the fluid to flow through bypass fluidconductor 30 bypassing fluid conductor 18 until fluid filter 12 can bereplaced.

Controller 28 can be configured to open bypass valve 32 based on apseudo-differential pressure measurement across filter 12. Controller 28can also be configured to generate an alert so as to notify a user thatfluid filter 12 is in need of replacement. Fluid conductor 18 isequipped with upstream pressure sensor 20 and downstream pressure sensor22. Upstream pressure sensor 20 senses an absolute pressure of theconducted fluid at a location upstream of fluid filter 12, whiledownstream pressure sensor 22 senses an absolute pressure of theconducted fluid at a location downstream of fluid filter 12. Each ofpressure sensors 20 and 22 provides a positive relation signal and anegative relation signal. Both the positive relation signals and thenegative relation signals are indicative of an absolute pressure asmeasured by pressure sensors 20 and 22. The positive relation signalsincrease with and/or in response to increasing absolute pressure, andthe negative relation signals decrease with and/or in response toincreasing absolute pressure. Upstream pressure sensor 20 provides itspositive relation signal on node 34 and its negative relation signal onnode 36. Downstream pressure sensor 22 provides its positive relationsignal on node 38 and its negative relation signal on node 40.

First difference calculator 24 receives the positive relation signals ofboth upstream pressure sensor 20 and downstream pressure sensor 22.First difference calculator 24 calculates a difference between thepositive relation signal provided by upstream pressure sensor 20 on node34 and the positive relation signal provided by downstream pressuresensor 22 on node 38. The calculated difference between the positiverelation signals of pressure sensors 20 and 22 is indicative of adifferential pressure across fluid filter 12. First differencecalculator 24 provides, based on the calculated difference, a firstdifference signal that is indicative of the differential pressure acrossfilter 12, on node 42.

Second difference calculator 26 receives the negative relation signalsof both upstream pressure sensor 20 and downstream pressure sensor 22.Second difference calculator 26 calculates a difference between thenegative relation signal provided by upstream pressure sensor 20 on node36 and the negative relation signal provided by downstream pressuresensor 22 on node 40. The calculated difference between the negativerelation signals of pressure sensors 20 and 22 is indicative of adifferential pressure across fluid filter 12. Second differencecalculator 26 provides, based on the calculated difference, a seconddifference signal that is indicative of the differential pressure acrossfilter 12, on node 44.

Sensor failure detector 27 also receives sensor signals on nodes 34, 36,38 and 40. Sensor failure detector 27 compares each of the signalsreceived on nodes 34, 36, 38 and 40 with one or more predeterminedthresholds. If one or more of the signals received on nodes 34, 36, 38and 40 are determined by sensor failure detector 27 to have failed,based on the comparison, then sensor failure detector 27 will generate afailure signal indicative of the node or nodes 34, 36, 38 or 40 on whichthe sensor signal is indicative of a failure. Sensor failure detector 27provides the generated failure signal on node 45.

Controller 28 receives both first difference signal on node 42 andsecond difference signal on node 44. Controller 28 also receives failuresignal on node 45. If controller 28 determines, based on the receivedfailure signal, that both the first and second difference signals areoperating properly, then controller 28 can use one or both of the firstand second difference signals to determine whether to open and/or closebypass valve 32. For example, if no failures pertaining to either thefirst or second difference signals are indicated by the failure signal,then controller 28 can average the first and second difference signals,for example. Controller 28 can then compare the average of the first andsecond difference signals with a predetermined threshold. If, forexample, the averaged first and second difference signals exceed thepredetermined threshold, indicating that the pressure difference acrossfilter 12 is greater than a predetermined value, then controller 28 cangenerate a control signal on node 46 configured to open bypass valve 32to augment the fluid conductivity of fluid conductor 18 with bypassfluid conductor 30.

If controller 28 determines, based on the failure signal, that one ofpositive and/or negative relation signals on nodes 34, 36, 38 and 40 areindicative of a failure, controller 28 can select an operative one offirst and second difference signals on nodes 42 and 44 to determinewhether to open and/or close bypass valve 32. For example, if a failuresignal received on node 45 is indicative of a failure of a sensorproviding signals affecting the first difference signal on node 42, thencontroller 28 can use the second difference signal on node 44 todetermine whether to open and/or close bypass valve 32. Similarly, if afailure signal received on node 45, for example, is indicative of afailure of a sensor providing signals affecting the second differencesignal on node 44, then controller 28 can use the first differencesignal on node 42 to determine whether to open and/or close bypass valve32. If a failure signal indicates that both the first difference signalon node 42 and the second difference signal on node 44 are compromised,then controller 28 can generate an alarm signal.

FIG. 2 is an electrical schematic of two absolute pressure sensorsconfigured to provide redundant measures of pseudo differentialpressure. In FIG. 2, absolute pressure sensors 20 and 22 are shownschematically. Each of absolute pressure sensors 20 and 22 is configuredas a Wheatstone bridge. Absolute pressure sensor 20 has four pressuretransducers 50, 52, 54 and 56. Pressure transducers 50 and 56 arenegative relation transducers (as indicated by the downward facingarrows), which decrease in resistance in response to increasingpressure. Pressure transducers 52 and 54 are positive relationtransducers (as indicated by the upward facing arrows) which increase inresistance in response to increasing pressure. Pressure transducers 50,52, 54 and 56 are configured as a Wheatstone bridge which provides fordifferential output signals on nodes 34 and 36.

Absolute pressure sensor 22 also has four pressure transducers 60, 62,64 and 66. Pressure transducers 60 and 66 are negative relationtransducers (as indicated by the downward facing arrows), which decreasein resistance in response to increasing pressure. Pressure transducers62 and 64 are positive relation transducers (as indicated by the upwardfacing arrows) which increase in resistance in response to increasingpressure. Pressure transducers 60, 62, 64 and 66 are configured as aWheatstone bridge which provides for differential output signals onnodes 38 and 40.

Two absolute pressure sensors can be configured to provide redundantpseudo-differential measurements if they provide a differential outputsignal. Thus, each of the two absolute pressure sensors does not requirefour pressure transducers as is depicted in FIG. 2. For example, in someembodiments, absolute pressure sensor 20 can have only positive relationpressure transducers 52 and 54. Instead of negative relation transducers50 and 56, resistors can be used in their respective locations withinthe Wheatstone bridge. In some embodiments, only negative relationtransducers 50 and 56 may be used, with resistors replacing positiverelation transducers 52 and 54. In another exemplary embodiment,positive relation transducer 52 and negative relation transducer 56 maybe used, with resistors replacing positive relation transducer 54 andnegative relation transducer 50, for example. In all of the aboveembodiments, differential signals are produced on nodes 34 and 36, eachindicative of a measurement of absolute pressure, one having a positiverelation and one having a negative relation with the absolute pressure.

In some embodiments, absolute pressure sensors can be manufactured usingpiezoresistive materials. Such piezoresistive materials have aresistivity that changes in response to mechanical strain. Thepiezoresistive material can be formed in various ways. For example, somepiezoresistive materials are deposited as thin films on a wafer orsubstrate. Some piezoresistive materials are formed by diffusing dopantspecies into a wafer or substrate. Some micro pressure sensors use anelastically deformable membrane as a member that is mechanicallyresponsive to pressure changes.

The elastically deformable membrane can be located above a referencecavity in which a reference pressure can be maintained. The membrane canthen deform in response to an externally applied pressure that isdifferent from the reference pressure. Such a pressure differential canelastically deform the membrane. In some embodiments, a substrate orbacking wafer may support the cavity and membrane to provide strengthand/or to reduce a packaging stress. In some applications, the backingwafer can have a pressure through-hole aligning to the cavity. When apressure through-hole is so provided, the reference pressure of thereference cavity can be provided by a fluid environment external to thecavity.

Piezoresistors can be formed on various surface regions of theelastically deformable membrane. Some of these surface regions canproduce tensile strain in the piezoresistors located thereon. Some ofthese surface regions can produce compressive strain in thepiezoresistors located thereon. By locating piezoresistors on bothtensile strain producing surface regions and compressive strainproducing surface regions, some piezoresistors have resistances thatincrease and some piezoresistors have resistances that decrease inresponse to elastic deformation. This measure of elastic deformation, inturn, can correspond to a difference between the externally appliedpressure and the reference pressure of the reference cavity.

Pseudo differential pressure sensing can be accomplished using two ofthese absolute pressure sensors. Each absolute pressure sensor can beexposed to a different one of two environments or two locations betweenwhich a measurement of differential pressure is sought. A differencebetween each of the two measurements of the two environments or twolocations can then be made by comparing a difference between theresistance changes of the piezoresistors of the two absolute pressuresensors. Each of the absolute pressure sensors can have two or morepiezoresistors, at least one located on a tensile strain producingsurface region and at least one located on a compressive strainproducing surface region. This configuration results in one of thepiezoresistors having a resistance that increases in response to anincreasing externally applied pressure and one of the piezoresistorshaving a resistance that decreases in response to an increasingexternally applied pressure.

The piezoresistors of the two absolute pressure sensors can be connectedas a Wheatstone bridge. Judiciously ordering the connection of thepiezoresistors of the two absolute pressure sensors in the Wheatstonebridge can be done so as to facilitate redundancy and robustness. Such ajudicious ordering of piezoresistors can permit a pseudo differentialpressure sensor to provide a signal indicative of a differentialpressure even in the event that one or more of the individualtransducers should fail. To accomplish such redundancy, each leg of theWheatstone bridge includes a piezoresistor from each of the two absolutepressure sensors. Thus, even if one of the legs should fail, thenon-failing leg provides a signal indicative of a differential pressure.

FIGS. 3A, 3B are side elevation views of an exemplary absolute pressuresensor, without and with a positive external pressure, respectively. InFIG. 3A, absolute pressure sensor 20 is shown cross-sectioned so as toreveal an inner reference cavity. Absolute pressure sensor 20 includesbacking wafer 72, substrate 74, and piezoresistors 50, 52, 54 and 56.Reference cavity 76 has been formed in substrate 74, creatingelastically deformable membrane 78 supported by adjacent supportstructures 80. Elastically deformable membrane 78 has a thickness 82 soas to permit a difference between an external pressure P_(external) anda reference pressure P_(reference) that exists within reference cavity76 to cause elastically deformable membrane 78 to deflect toward cavityfloor 84. In some embodiments a deflection limiter can provide amechanical stop to limit the amount of deflection of elasticallydeformable membrane 78.

Each of piezoresistors 50, 52, 54 and 56 is intimately connected to topsurface 86 of elastically deformable membrane 80. Because piezoresistors50, 52, 54 and 56 are intimately connected to top surface 86 ofelastically deformable membrane 78, piezoresistors 50, 52, 54 and 56will deform commensurate with a deformation of the regions of topsurface 86 to which piezoresistors 50, 52, 54 and 56 adhere. Thus, whenelastically deformable membrane 20 deforms, so do piezoresistors 50, 52,54 and 56. When piezoresistors 50, 52, 54 and 56 deform (e.g., undergocompressive and/or tensile strain), resistances of piezoresistors 50,52, 54 and 56 change in response to deformation of piezoresistors 50,52, 54 and 56.

Piezoresistors 50, 52, 54 and 56 are located on top surface 86 ofelastically deformable membrane 78 in order to deform in response todeformations of elastically deformable membrane 78. Top surface 86 canhave a layer of a dielectric material such as, for example, silicondioxide and/or silicon nitride. Piezoresistors 50 and 56 are located onregions of top surface 86 where piezoresistors 50 and 56 will experiencetensile strain in response to external pressure P_(external) exceedingreference pressure P_(reference). Piezoresistors 52 and 54 are locatedon regions of top surface 90 where piezoresistors 52 and 54 willexperience compressive strain in response to external pressureP_(external) exceeding reference pressure P_(reference).

FIG. 3B depicts absolute pressure sensor 20 shown in FIG. 3A, but in adeformed state in response to external pressure P_(external) exceedingreference pressure P_(reference) of reference cavity 76. Such adifference in pressures has caused elastically deformable membrane 78 todeform and deflect toward cavity floor 84 of reference cavity 76. In thedepicted state, each of ends 78a, 78b of deformable membrane 78 tracesan S-shape, having convex portions 78 c and concave portions 78 d.Convex portions 78 c and concave portions 78 d are so described from theperspective of looking down upon top surface 86 of absolute pressuresensor 20.

When elastically deformable membrane 78 is deformed as depicted in FIG.3B, an intimate interface between piezoresistors 50, 52, 54 and 56 andelastically deformable membrane 78 causes bottom portions ofpiezoresistors that are proximate these intimate interfaces to deform ina similar fashion as the deformation of elastically deformable membrane78. Such convex and concave deformations are then projected throughoutthickness 82 of piezoresistors 50, 52, 54 and 56, respectively. Theprojections of convex potions 78 c cause top portions of piezoresistors50 and 56 to be in tensile stress. The projections of concave portions78 d cause top portions of piezoresistors 52 and 54 to be in compressivestress.

Piezoresistors 50 and 56 that are in tensile stress have resistancesthat change with a first polarity. Piezoresistors 52 and 54 that are incompressive stress have resistances that change with a second polarity,opposite that of the first polarity. For example, in some embodiments,resistance along lengths of piezoresistors 50 and 56 may increase whenpiezoresistors 50 and 56 are in tensile stress, and resistance along thelengths of piezoresistors 52 and 54 may decrease when piezoresistors 52and 54 are in compressive stress. In some embodiments, piezoresistors 50and 56 may be series connected so as to increase signal strength of afirst polarity signal. Similarly piezoresistors 52 and 54 may be seriesconnected to increase signal strength of a second polarity signal.

Various piezoresistive materials may have various piezoresistivecoefficients relating strain to signal magnitude and signal polarity.Some materials may increase in resistance under tensile strain anddecrease in resistance under compressive strain. Other materials myincrease in resistance under compressive strain and decrease inresistance under tensile strain. Henceforth the polarity of thepiezoresistive coefficient will be indicated by an arrow drawn across aresistor. Piezoresistors having resistances that increase in response toincreasing pressure will be represented by an up-arrow. Piezoresistorshaving resistances that decrease in response to increasing pressure willbe represented by a down-arrow. The arrows annotating piezoresistorsymbols that are pointed in the same direction to one another indicatepiezoresistors that have the same polarity of resistance change inresponse to changes in external pressure P_(external).

FIG. 4 is a perspective view of an exemplary pseudo differentialpressure sensor configured as a Wheatstone bridge. In FIG. 4, pseudodifferential pressure sensor 98 includes first absolute pressure sensor20 and second absolute pressure sensor 22. First absolute pressuresensor 20 includes piezoresistors 50, 52, 54 and 56. Similarly, secondabsolute pressure sensor 22 includes piezoresistors 60, 62, 64 and 66.

Piezoresistors 50 and 52 of absolute pressure sensor 20 andpiezoresistors 60 and 62 of absolute pressure sensor 22 are electricallyconnected as Wheatstone bridge 100. Wheatstone bridge 100 includes firstvoltage-divider leg 102 and second voltage-divider leg 104. Firstvoltage-divider leg 102 includes piezoresistors 50 and 52 of firstabsolute pressure sensor 20 series connected at first output nodeOUTPUT_1 (or Vo CH1+). Second voltage-divider leg 104 includespiezoresistor 60 and 62 of second absolute pressure sensor 22 seriesconnected at second output node OUTPUT_2 (or Vo CH1−). Each of thepiezoresistors sharing a voltage-divider leg 102 or 104 has the samerelation (e.g., relation to absolute pressure) of signal with respect tothe absolute pressure to which it responds, albeit each voltage-dividerleg pertains to a different absolute pressure sensor 20 and 22,respectively. The arrangement of the opposite polarities of resistancechange in the two voltage divider legs 102 and 104, however, isdifferent, one from the other. Such a configuration of polarities oftransducers within voltage divider legs ensures that OUTPUT_1 will havethe same relation to absolute pressure as OUTPUT_2 has to absolutepressure. In this way, a difference between the signals produced atOUTPUT_1 and OUTPUT_2 will represent a pseudo-differential pressurebetween Presssure_1 and Pressure_2.

Piezoresistors 54, 56, 64 and 66 can be electrically connected in afashion that is similar to the electrical connection of piezoresistors50, 52, 60 and 62. Such a connection can provide a redundant measure ofpseudo-differential pressure. In some embodiments, piezoresistors 54,56, 64 and 66 can be electrically connected as a second Wheatstonebridge for such redundancy.

The following are non-exclusive descriptions of possible embodiments ofthe present invention.

An exemplary embodiment relates to a system for providing redundantmeasurement of pseudo differential pressure. The system includes a firstabsolute-pressure sensor exposed to a first environment. The firstabsolute-pressure sensor includes a plurality of pressure transducersconfigured in a first Wheatstone bridge. The first Wheatstone bridge hasfirst and second output nodes that operationally generate first andsecond output signals that increase and decrease, respectively, inresponse to increasing pressure of the first environment. The systemincludes a second absolute-pressure sensor exposed to a secondenvironment. The second absolute-pressure sensor includes a plurality ofpressure transducers configured in a second Wheatstone bridge. Thesecond Wheatstone bridge has third and fourth output nodes thatoperationally generate first and second output signals that increase anddecrease, respectively, in response to increasing pressure of the secondenvironment. The system includes a first difference calculatorelectrically coupled to the first and third output nodes of the firstand second absolute-pressure sensors, respectively. The first differencecalculator generates, based on a difference between the first and thirdoutput signals of the first and third output nodes, a first measurementsignal indicative of a pressure difference between the first and secondenvironments. The system also includes a second difference calculatorelectrically coupled to the second and fourth output nodes of the firstand second absolute-pressure sensors, respectively. The seconddifference calculator generates, based on a difference between thesecond and fourth output signals of the second and fourth output nodes,a second measurement signal indicative of the pressure differencebetween the first and second environments.

The system of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

A further embodiment of the foregoing system, wherein each of theplurality of pressure transducers of the first absolute pressure sensorcan be a piezo-resistive transducer, and each of the plurality ofpressure transducers of the second absolute pressure sensor can be apiezo-resistive transducer.

A further embodiment of any of the foregoing systems, wherein each ofthe first and second absolute-pressure sensors can include anelastically deformable membrane configured to deform in response toexposure to an environment having a pressure. Each of the first andsecond absolute-pressure sensors can further include a firstpiezoresistor located on the elastically deformable membrane at a firstregion where increasing the pressure of the environment produces anincreasing tensile strain in the first piezoresistor. Each of the firstand second absolute-pressure sensors can further include a secondpiezoresistor located on the elastically deformable membrane at a secondregion where increasing the pressure of the environment produces anincreasing compressive strain in the second piezoresistor.

A further embodiment of any of the foregoing systems, wherein each ofthe first and second absolute-pressure sensors can further include athird piezoresistor located on the elastically deformable membrane at athird region where increasing the pressure of the environment producesan increasing tensile strain in the third piezoresistor. Each of thefirst and second absolute-pressure sensors can further include a fourthpiezoresistor located on the elastically deformable membrane at a fourthregion where increasing the pressure of the environment produces anincreasing compressive strain in the fourth piezoresistor.

A further embodiment of any of the foregoing systems, wherein the firstand second piezoresistors of each of the first and secondabsolute-pressure sensors can be electrically connected as a firstvoltage-divider leg of the first and second Wheatstone bridges. Thethird and fourth piezoresistors of each of the first and secondabsolute-pressure sensors can be electrically connected as a secondvoltage-divider leg of the first and second Wheatstone bridges.

A further embodiment of any of the foregoing systems can further includea control system configured to supply operating power to the first andsecond absolute-pressure sensors, and to receive, from the first andsecond difference calculators, the first and second measurement signals,respectively.

A further embodiment of any of the foregoing systems, wherein thecontrol system can be further configured to evaluate whether each of thefirst and second measurement signals are within a predetermined signalrange corresponding to a normal operating range.

A further embodiment of any of the foregoing systems, wherein, upondetermining that only one of the first and the second measurementsignals is within the predetermined signal range, the control system cangenerate a measurement signal indicative of the pressure differencebetween the first and second environments based on one of the first andsecond output signals that is within the predetermined signal range.

A further embodiment of any of the foregoing systems can further includea flow tube having a filter element separating a first end and a secondend. The first absolute-pressure sensor can be in fluid communicationwith the first end of the flow tube. The second absolute-pressure sensorcan be in fluid communication with the second side of the flow tube.

Some embodiments relate to a system for providing redundant measurementof pseudo differential pressure. The system includes first and secondabsolute-pressure sensors configured to measure a pressure of first andsecond environments, respectively. Each of the first and secondabsolute-pressure sensors includes an elastically deformable membraneconfigured to deform in response to exposure to an environment having apressure. Each of the first and second absolute-pressure sensorsincludes a first piezoresistor located on a first surface region of theelastically deformable membrane. The first surface region becomingincreasingly convex in response to increasing pressure. Each of thefirst and second absolute-pressure sensors includes a secondpiezoresistor located on a second surface region of the elasticallydeformable membrane. The second surface region becomes increasinglyconcave in response to increasing pressure. The first piezoresistors ofboth the first and second absolute-pressure sensors are electricallyconfigured in a first Wheatstone bridge operatively generating a firstmeasurement signal indicative of a pressure difference between the firstand second environments. The second piezoresistors of both the first andsecond absolute-pressure sensors are electrically configured in a secondWheatstone bridge operatively generating a second measurement signalindicative of the pressure difference between the first and secondenvironments.

The system of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

A further embodiment of the foregoing system, wherein each of the firstand second absolute-pressure sensors can further include a thirdpiezoresistor located on a third surface region of the elasticallydeformable membrane. The first surface region can become increasinglyconvex in response to increasing pressure. Each of the first and secondabsolute-pressure sensors can further include a fourth piezoresistorlocated on a fourth surface region of the elastically deformablemembrane. The second surface region becoming increasingly concave inresponse to increasing pressure.

A further embodiment of any of the foregoing systems, wherein the firstand fourth piezoresistors of each of the first and secondabsolute-pressure sensors can form a first voltage divider, and thesecond and third piezoresistors of each the first and secondabsolute-pressure sensors can form a second voltage divider. The firstWheatstone bridge can include the first voltage dividers of the firstand second absolute-pressure sensors and the second Wheatstone bridgecan include the second voltage dividers of each of the first and secondabsolute-pressure sensors.

A further embodiment of any of the foregoing systems can further includea control system configured to supply operating power to the first andsecond absolute-pressure sensors, and to receive, from the first andsecond Wheatstone bridges, the first and second measurement signals,respectively.

A further embodiment of any of the foregoing systems, wherein thecontrol system can be further configured to evaluate whether each of thefirst and second measurement signals are within a predetermined signalrange corresponding to a normal operating range.

A further embodiment of any of the foregoing systems, wherein, upondetermining that only one of the first and the second measurementsignals is within the predetermined signal range, the control system cangenerate a measurement signal indicative of the pressure differencebetween the first and second environments based on one of the first andsecond output signals that is within the predetermined signal range.

A further embodiment of any of the foregoing systems can further includea flow tube having a filter element separating a first end and a secondend. The first absolute-pressure sensor can be in fluid communicationwith the first end of the flow tube. The second absolute-pressure sensorcan be in fluid communication with the second side of the flow tube.

Some embodiments relate to a method for providing redundant measurementof pseudo differential pressure. The method includes exposing a firstabsolute pressure sensor to the first environment having a firstpressure. The method includes exposing a second absolute pressure sensorto the second environment having a second pressure. The method includesgenerating complementary first and second output signals, eachindicative of the first pressure of the first environment. The methodincludes generating complementary third and fourth output signals, eachindicative of the second pressure of the second environment. The methodincludes calculating a first difference signal between the first andthird output signals. The method includes calculating a seconddifference signal between the second and fourth output signals. Themethod includes selecting a measurement signal from among the first andsecond difference signals for use as a signal indicative of a pressuredifference between the first and second environments. The method alsoincludes outputting the selected measurement signal.

The method of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

A further embodiment of the foregoing method, wherein selecting fromamong the first and second difference signals can include comparing eachof the first and second difference signals with each of a high referencesignal and a low reference signal. Selecting from among the first andsecond difference signals can further include selecting one of the firstand second difference signals that is between the high reference signaland the low reference signal.

A further embodiment of any of the foregoing methods, wherein selectingfrom among the first and second difference signals can further includeselecting, if only one of the first and the second difference signals isbetween the high and the low reference signals, the one of the first andthe second difference signals that is between the high and the lowreference signals.

A further embodiment of any of the foregoing methods can further includegenerating, in response to neither the first nor the second differencesignal being between the high and the low reference signals, an alarmsignal.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

1. A system for providing redundant measurement of pseudo differentialpressure, the system comprising: a first absolute-pressure sensorexposed to a first environment, the first absolute-pressure sensorincluding a plurality of pressure transducers configured in a firstWheatstone bridge, the first Wheatstone bridge having first and secondoutput nodes that operationally generate first and second output signalsthat increase and decrease, respectively, in response to increasingpressure of the first environment; a second absolute-pressure sensorexposed to a second environment, the second absolute-pressure sensorincluding a plurality of pressure transducers configured in a secondWheatstone bridge, the second Wheatstone bridge having third and fourthoutput nodes that operationally generate first and second output signalsthat increase and decrease, respectively, in response to increasingpressure of the second environment; a first difference calculatorelectrically coupled to the first and third output nodes of the firstand second absolute-pressure sensors, respectively, the first differencecalculator generating, based on a difference between the first and thirdoutput signals of the first and third output nodes, a first measurementsignal indicative of a pressure difference between the first and secondenvironments; and a second difference calculator electrically coupled tothe second and fourth output nodes of the first and secondabsolute-pressure sensors, respectively, the second differencecalculator generating, based on a difference between the second andfourth output signals of the second and fourth output nodes, a secondmeasurement signal indicative of the pressure difference between thefirst and second environments.
 2. The system of claim 1, wherein each ofthe plurality of pressure transducers of the first absolute pressuresensor is a piezo-resistive transducer, and each of the plurality ofpressure transducers of the second absolute pressure sensor is apiezo-resistive transducer.
 3. The system of claim 1, wherein each ofthe first and second absolute-pressure sensors comprises: an elasticallydeformable membrane configured to deform in response to exposure to anenvironment having a pressure; a first piezoresistor located on theelastically deformable membrane at a first region where increasing thepressure of the environment produces an increasing tensile strain in thefirst piezoresistor; and a second piezoresistor located on theelastically deformable membrane at a second region where increasing thepressure of the environment produces an increasing compressive strain inthe second piezoresistor.
 4. The system of claim 3, wherein each of thefirst and second absolute-pressure sensors further comprises: a thirdpiezoresistor located on the elastically deformable membrane at a thirdregion where increasing the pressure of the environment produces anincreasing tensile strain in the third piezoresistor; and a fourthpiezoresistor located on the elastically deformable membrane at a fourthregion where increasing the pressure of the environment produces anincreasing compressive strain in the fourth piezoresistor.
 5. The systemof claim 4, wherein the first and second piezoresistors of each of thefirst and second absolute-pressure sensors are electrically connected asa first voltage-divider leg of the first and second Wheatstone bridges,wherein the third and fourth piezoresistors of each of the first andsecond absolute-pressure sensors are electrically connected as a secondvoltage-divider leg of the first and second Wheatstone bridges.
 6. Thesystem of claim 1, further comprising a control system configured tosupply operating power to the first and second absolute-pressuresensors, and to receive, from the first and second differencecalculators, the first and second measurement signals, respectively. 7.The system of claim 6, wherein the control system is further configuredto evaluate whether each of the first and second measurement signals arewithin a predetermined signal range corresponding to a normal operatingrange.
 8. The system of claim 7, wherein, upon determining that only oneof the first and the second measurement signals is within thepredetermined signal range, the control system generates a measurementsignal indicative of the pressure difference between the first andsecond environments based on one of the first and second output signalsthat is within the predetermined signal range.
 9. The system of claim 1,further comprising a flow tube having a filter element separating afirst end and a second end, the first absolute-pressure sensor in fluidcommunication with the first end of the flow tube, the secondabsolute-pressure sensor in fluid communication with the second side ofthe flow tube.
 10. A system for providing redundant measurements ofpseudo differential pressure, the system comprising: first and secondabsolute-pressure sensors configured to measure a pressure of first andsecond environments, respectively, each of the first and secondabsolute-pressure sensors comprising: an elastically deformable membraneconfigured to deform in response to exposure to an environment having apressure; a first piezoresistor located on a first surface region of theelastically deformable membrane, the first surface region becomingincreasingly convex in response to increasing pressure; and a secondpiezoresistor located on a second surface region of the elasticallydeformable membrane, the second surface region becoming increasinglyconcave in response to increasing pressure, wherein the firstpiezoresistors of both the first and second absolute-pressure sensorsare electrically configured in a first Wheatstone bridge operativelygenerating a first measurement signal indicative of a pressuredifference between the first and second environments, wherein the secondpiezoresistors of both the first and second absolute-pressure sensorsare electrically configured in a second Wheatstone bridge operativelygenerating a second measurement signal indicative of the pressuredifference between the first and second environments.
 11. The system ofclaim 10, wherein each of the first and second absolute-pressure sensorsfurther comprises: a third piezoresistor located on a third surfaceregion of the elastically deformable membrane, the first surface regionbecoming increasingly convex in response to increasing pressure; and afourth piezoresistor located on a fourth surface region of theelastically deformable membrane, the second surface region becomingincreasingly concave in response to increasing pressure.
 12. The systemof claim 11, wherein the first and fourth piezoresistors of each of thefirst and second absolute-pressure sensors form a first voltage divider,and the second and third piezoresistors of each the first and secondabsolute-pressure sensors form a second voltage divider, the firstWheatstone bridge including the first voltage dividers of the first andsecond absolute-pressure sensors and the second Wheatstone bridgeincluding the second voltage dividers of each of the first and secondabsolute-pressure sensors.
 13. The system of claim 10, furthercomprising a control system configured to supply operating power to thefirst and second absolute-pressure sensors, and to receive, from thefirst and second Wheatstone bridges, the first and second measurementsignals, respectively.
 14. The system of claim 13, wherein the controlsystem is further configured to evaluate whether each of the first andsecond measurement signals are within a predetermined signal rangecorresponding to a normal operating range.
 15. The system of claim 14,wherein, upon determining that only one of the first and the secondmeasurement signals is within the predetermined signal range, thecontrol system generates a measurement signal indicative of the pressuredifference between the first and second environments based on one of thefirst and second output signals that is within the predetermined signalrange.
 16. The system of claim 10, further comprising a flow tube havinga filter element separating a first end and a second end, the firstabsolute-pressure sensor in fluid communication with the first end ofthe flow tube, the second absolute-pressure sensor in fluidcommunication with the second side of the flow tube.
 17. A method forproviding redundant measurements of pseudo differential pressure, themethod comprising: exposing a first absolute pressure sensor to thefirst environment having a first pressure; exposing a second absolutepressure sensor to the second environment having a second pressure;generating complementary first and second output signals, eachindicative of the first pressure of the first environment; generatingcomplementary third and fourth output signals, each indicative of thesecond pressure of the second environment; calculating a firstdifference signal between the first and third output signals;calculating a second difference signal between the second and fourthoutput signals; selecting a measurement signal from among the first andsecond difference signals for use as a signal indicative of a pressuredifference between the first and second environments; and outputting theselected measurement signal.
 18. The method of claim 17, whereinselecting from among the first and second difference signals comprises:comparing each of the first and second difference signals with each of ahigh reference signal and a low reference signal; and selecting one ofthe first and second difference signals that is between the highreference signal and the low reference signal.
 19. The method of claim18, wherein selecting from among the first and second difference signalsfurther comprises: selecting, if only one of the first and the seconddifference signals is between the high and the low reference signals,the one of the first and the second difference signals that is betweenthe high and the low reference signals.
 20. The method of claim 18,further comprising: generating, in response to neither the first nor thesecond difference signal being between the high and the low referencesignals, an alarm signal.